01 - Heat the vegetable oil in a large skillet over medium heat until it shimmers.
02 - Add the chopped onion and sauté for 3 to 4 minutes, stirring occasionally, until translucent and softened.
03 - Stir in the minced garlic and chopped chiles. Cook for 2 minutes until fragrant and the chiles begin to soften.
04 - Add the diced tomatoes and cook, stirring frequently, for 5 minutes until they break down and release their juices, forming a rustic sauce.
05 - Add the cubed potatoes, ground cumin, salt, and black pepper. Stir thoroughly to coat all the potatoes evenly in the sauce.
06 - Pour in ¾ cup water, just enough to partially cover the potatoes. Bring to a simmer, then cover the skillet and cook for 15 to 20 minutes, stirring occasionally, until the potatoes are fork-tender and the sauce has thickened.
07 - Taste and adjust the salt and pepper as needed. Garnish with fresh cilantro if desired. Serve hot with warm tortillas or use as a taco filling.